Polymeric coatings are widely used in a variety of applications for both protective and decorative purposes. The requirements of maintaining good appearance even after exposure to weathering and other forms of attack are particularly stringent in the field of automotive coatings. Other properties that are desirable for coatings, such as automotive coatings, include good tensile strength, scratch and mar resistance, flexibility, and adhesion to a variety substrates and coatings.
Many polymer coating compositions are curable coating compositions. By this it is meant that an additional reaction, such as a crosslinking reaction, takes place after the coating is applied to a substrate. In order to provide coatings having an optimum combination of the above-described properties, many curable coating compositions in recent years have utilized the so-called carboxy-epoxy cure mechanism. This type of curing depends on a reaction between a compound having epoxy-functional group(s) and a curing agent having carboxy-functional group(s). By way of a ring-opening reaction between the carboxy groups and the epoxy groups, a matrix of chemical bonds is formed, resulting in a hard cured coating.
One such carboxy-epoxy-cure coating composition is described in U.S. Pat. No. 4,699,814. This patent describes a coating composition comprising (a) an epoxy-functional polyurethane resin that is prepared by reacting an isocyanate with a hydroxyl-functional polyepoxide having two or more epoxy groups per molecule, and (b) a polyacid, anhydride, or polyamine curing agent.
Many coating compositions that are cured via a carboxy-epoxy cure mechanism exhibit film properties that are less than desirable. For example, some compositions may result in films that do not exhibit sufficiently high strength or hardness. Other compositions may result in films that are not sufficiently flexible. Still other compositions may result in films that are brittle. Other problems, such as wrinkling, or poor adhesion (which can result in delamination) may also be experienced.
It is thus an object of this invention to provide a coating composition that utilizes the carboxy-epoxy cure mechanism, and that is capable of producing a cured film coating having the desirable film properties described above.